/**
 * **************** Copyright (C) *****************
 * <p/>
 * Version       Date            Author
 * ─────────────────────────────────────
 * V1.0        2016/9/1         yellowlgx
 * <p/>
 * **************** End of Head *******************
 */
package com.skyworth.ui.api;

import android.content.Context;
import android.hardware.SensorManager;
import android.util.Log;
import android.view.ViewConfiguration;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;

/**
 * @author : yellowlgx
 * @ClassName OverScroller
 * @Description : TODO
 * @date : 2016/9/1 18:50
 */
public class OverScroller
{
    private int mMode;

    private final SplineOverScroller mScrollerX;
    private final SplineOverScroller mScrollerY;

    private Interpolator mInterpolator;

    private final boolean mFlywheel;

    private static int DEFAULT_DURATION = 250;
    private static final int SCROLL_MODE = 0;
    private static final int FLING_MODE = 1;

    private OnScollStateListener mListener;

    public interface OnScollStateListener
    {
        public void onScrollStart();

        public void onScrollStop();
    }

    /**
     * Creates an OverScroller with a viscous fluid scroll interpolator and flywheel.
     *
     * @param context
     */
    public OverScroller(Context context)
    {
        this(context, null);
    }

    /**
     * Creates an OverScroller with flywheel enabled.
     *
     * @param context      The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     *                     be used.
     */
    public OverScroller(Context context, Interpolator interpolator)
    {
        this(context, interpolator, true);
    }

    /**
     * Creates an OverScroller.
     *
     * @param context      The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     *                     be used.
     * @param flywheel     If true, successive fling motions will keep on increasing scroll speed.
     * @hide
     */
    public OverScroller(Context context, Interpolator interpolator, boolean flywheel)
    {
        if (interpolator == null)
        {
            mInterpolator = new ViscousFluidInterpolator();
        } else
        {
            mInterpolator = interpolator;
        }
        mFlywheel = flywheel;
        mScrollerX = new SplineOverScroller(context);
        mScrollerY = new SplineOverScroller(context);
    }

    /**
     * Creates an OverScroller with flywheel enabled.
     *
     * @param context            The context of this application.
     * @param interpolator       The scroll interpolator. If null, a default (viscous) interpolator will
     *                           be used.
     * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the
     *                           velocity which is preserved in the bounce when the horizontal edge is
     *                           reached. A null value
     *                           means no bounce. This behavior is no longer supported and this coefficient
     *                           has no effect.
     * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This
     *                           behavior is no longer supported and this coefficient has no effect.
     *                           !deprecated Use {!link #OverScroller(Context, Interpolator, boolean)}
     *                           instead.
     */
    public OverScroller(Context context, Interpolator interpolator,
                        float bounceCoefficientX, float bounceCoefficientY)
    {
        this(context, interpolator, true);
    }

    /**
     * Creates an OverScroller.
     *
     * @param context            The context of this application.
     * @param interpolator       The scroll interpolator. If null, a default (viscous) interpolator will
     *                           be used.
     * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the
     *                           velocity which is preserved in the bounce when the horizontal edge is
     *                           reached. A null value
     *                           means no bounce. This behavior is no longer supported and this coefficient
     *                           has no effect.
     * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This
     *                           behavior is no longer supported and this coefficient has no effect.
     * @param flywheel           If true, successive fling motions will keep on increasing scroll speed.
     *                           !deprecated Use {!link OverScroller(Context, Interpolator, boolean)} instead.
     */
    public OverScroller(Context context, Interpolator interpolator,
                        float bounceCoefficientX, float bounceCoefficientY, boolean flywheel)
    {
        this(context, interpolator, flywheel);
    }

    public void setOnScollStateListener(OnScollStateListener listener)
    {
        mListener = listener;
    }

    void setInterpolator(Interpolator interpolator)
    {
        if (interpolator == null)
        {
            mInterpolator = new ViscousFluidInterpolator();
        } else
        {
            mInterpolator = interpolator;
        }
    }

    /**
     * The amount of friction applied to flings. The default value
     * is {@link ViewConfiguration#getScrollFriction}.
     *
     * @param friction A scalar dimension-less value representing the coefficient of
     *                 friction.
     */
    public final void setFriction(float friction)
    {
        mScrollerX.setFriction(friction);
        mScrollerY.setFriction(friction);
    }

    /**
     * Returns whether the scroller has finished scrolling.
     *
     * @return True if the scroller has finished scrolling, false otherwise.
     */
    public final boolean isFinished()
    {
        return mScrollerX.mFinished && mScrollerY.mFinished;
    }

    /**
     * Force the finished field to a particular value. Contrary to
     * {@link #abortAnimation()}, forcing the animation to finished
     * does NOT cause the scroller to move to the final x and y
     * position.
     *
     * @param finished The new finished value.
     */
    public final void forceFinished(boolean finished)
    {
        mScrollerX.mFinished = mScrollerY.mFinished = finished;
    }

    /**
     * Returns the current X offset in the scroll.
     *
     * @return The new X offset as an absolute distance from the origin.
     */
    public final int getCurrX()
    {
        return mScrollerX.mCurrentPosition;
    }

    /**
     * Returns the current Y offset in the scroll.
     *
     * @return The new Y offset as an absolute distance from the origin.
     */
    public final int getCurrY()
    {
        return mScrollerY.mCurrentPosition;
    }

    /**
     * Returns the absolute value of the current velocity.
     *
     * @return The original velocity less the deceleration, norm of the X and Y velocity vector.
     */
    public float getCurrVelocity()
    {
        return (float) Math.hypot(mScrollerX.mCurrVelocity, mScrollerY.mCurrVelocity);
    }

    /**
     * Returns the start X offset in the scroll.
     *
     * @return The start X offset as an absolute distance from the origin.
     */
    public final int getStartX()
    {
        return mScrollerX.mStart;
    }

    /**
     * Returns the start Y offset in the scroll.
     *
     * @return The start Y offset as an absolute distance from the origin.
     */
    public final int getStartY()
    {
        return mScrollerY.mStart;
    }

    /**
     * Returns where the scroll will end. Valid only for "fling" scrolls.
     *
     * @return The final X offset as an absolute distance from the origin.
     */
    public final int getFinalX()
    {
        return mScrollerX.mFinal;
    }

    /**
     * Returns where the scroll will end. Valid only for "fling" scrolls.
     *
     * @return The final Y offset as an absolute distance from the origin.
     */
    public final int getFinalY()
    {
        return mScrollerY.mFinal;
    }

    /**
     * Returns how long the scroll event will take, in milliseconds.
     *
     * @return The duration of the scroll in milliseconds.
     * @hide Pending removal once nothing depends on it
     * @deprecated OverScrollers don't necessarily have a fixed duration.
     * This function will lie to the best of its ability.
     */
    @Deprecated
    public final int getDuration()
    {
        return Math.max(mScrollerX.mDuration, mScrollerY.mDuration);
    }

    /**
     * Extend the scroll animation. This allows a running animation to scroll
     * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}.
     *
     * @param extend Additional time to scroll in milliseconds.
     * @hide Pending removal once nothing depends on it
     * @see #setFinalX(int)
     * @see #setFinalY(int)
     * @deprecated OverScrollers don't necessarily have a fixed duration.
     * Instead of setting a new final position and extending
     * the duration of an existing scroll, use startScroll
     * to begin a new animation.
     */
    @Deprecated
    public void extendDuration(int extend)
    {
        mScrollerX.extendDuration(extend);
        mScrollerY.extendDuration(extend);
    }

    /**
     * Sets the final position (X) for this scroller.
     *
     * @param newX The new X offset as an absolute distance from the origin.
     * @hide Pending removal once nothing depends on it
     * @see #extendDuration(int)
     * @see #setFinalY(int)
     * @deprecated OverScroller's final position may change during an animation.
     * Instead of setting a new final position and extending
     * the duration of an existing scroll, use startScroll
     * to begin a new animation.
     */
    @Deprecated
    public void setFinalX(int newX)
    {
        mScrollerX.setFinalPosition(newX);
    }

    /**
     * Sets the final position (Y) for this scroller.
     *
     * @param newY The new Y offset as an absolute distance from the origin.
     * @hide Pending removal once nothing depends on it
     * @see #extendDuration(int)
     * @see #setFinalX(int)
     * @deprecated OverScroller's final position may change during an animation.
     * Instead of setting a new final position and extending
     * the duration of an existing scroll, use startScroll
     * to begin a new animation.
     */
    @Deprecated
    public void setFinalY(int newY)
    {
        mScrollerY.setFinalPosition(newY);
    }

    /**
     * Call this when you want to know the new location. If it returns true, the
     * animation is not yet finished.
     */
    public boolean computeScrollOffset()
    {
        if (isFinished())
        {
            return false;
        }

        switch (mMode)
        {
            case SCROLL_MODE:
                long time = AnimationUtils.currentAnimationTimeMillis();
                // Any scroller can be used for time, since they were started
                // together in scroll mode. We use X here.
                final long elapsedTime = time - mScrollerX.mStartTime;

                final int duration = mScrollerX.mDuration;
                if (elapsedTime < duration)
                {
                    final float q = mInterpolator.getInterpolation(elapsedTime / (float) duration);
                    mScrollerX.updateScroll(q);
                    mScrollerY.updateScroll(q);
                } else
                {
                    abortAnimation();
                }
                break;

            case FLING_MODE:
                if (!mScrollerX.mFinished)
                {
                    if (!mScrollerX.update())
                    {
                        if (!mScrollerX.continueWhenFinished())
                        {
                            mScrollerX.finish();
                        }
                    }
                }

                if (!mScrollerY.mFinished)
                {
                    if (!mScrollerY.update())
                    {
                        if (!mScrollerY.continueWhenFinished())
                        {
                            mScrollerY.finish();
                            if (mListener != null)
                                mListener.onScrollStop();
                        }
                    }
                }

                break;
        }

        return true;
    }

    /**
     * Start scrolling by providing a starting point and the distance to travel.
     * The scroll will use the default value of 250 milliseconds for the
     * duration.
     *
     * @param startX Starting horizontal scroll offset in pixels. Positive
     *               numbers will scroll the content to the left.
     * @param startY Starting vertical scroll offset in pixels. Positive numbers
     *               will scroll the content up.
     * @param dx     Horizontal distance to travel. Positive numbers will scroll the
     *               content to the left.
     * @param dy     Vertical distance to travel. Positive numbers will scroll the
     *               content up.
     */
    public void startScroll(int startX, int startY, int dx, int dy)
    {
        startScroll(startX, startY, dx, dy, DEFAULT_DURATION);
    }

    /**
     * Start scrolling by providing a starting point and the distance to travel.
     *
     * @param startX   Starting horizontal scroll offset in pixels. Positive
     *                 numbers will scroll the content to the left.
     * @param startY   Starting vertical scroll offset in pixels. Positive numbers
     *                 will scroll the content up.
     * @param dx       Horizontal distance to travel. Positive numbers will scroll the
     *                 content to the left.
     * @param dy       Vertical distance to travel. Positive numbers will scroll the
     *                 content up.
     * @param duration Duration of the scroll in milliseconds.
     */
    public void startScroll(int startX, int startY, int dx, int dy, int duration)
    {
        mMode = SCROLL_MODE;
        mScrollerX.startScroll(startX, dx, duration);
        mScrollerY.startScroll(startY, dy, duration);
        Log.v("ThemeController", "dy---> " + dy + "  dx---> " + dx);
        if (mListener != null)
            mListener.onScrollStart();
    }

    public void setScrollDuration(int duration, boolean isDefualt)
    {
        if (isDefualt)
        {
            DEFAULT_DURATION = 250;
//            mScrollerX.setScrollDuration(DEFAULT_DURATION);
//            mScrollerY.setScrollDuration(DEFAULT_DURATION);
        } else
        {
            DEFAULT_DURATION = duration;
//            mScrollerX.setScrollDuration(duration);
//            mScrollerY.setScrollDuration(duration);
        }
    }

    /**
     * Call this when you want to 'spring back' into a valid coordinate range.
     *
     * @param startX Starting X coordinate
     * @param startY Starting Y coordinate
     * @param minX   Minimum valid X value
     * @param maxX   Maximum valid X value
     * @param minY   Minimum valid Y value
     * @param maxY   Minimum valid Y value
     * @return true if a springback was initiated, false if startX and startY were
     * already within the valid range.
     */
    public boolean springBack(int startX, int startY, int minX, int maxX, int minY, int maxY)
    {
        mMode = FLING_MODE;

        // Make sure both methods are called.
        final boolean spingbackX = mScrollerX.springback(startX, minX, maxX);
        final boolean spingbackY = mScrollerY.springback(startY, minY, maxY);
        return spingbackX || spingbackY;
    }

    public void fling(int startX, int startY, int velocityX, int velocityY,
                      int minX, int maxX, int minY, int maxY)
    {
        fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY, 0, 0);
    }

    /**
     * Start scrolling based on a fling gesture. The distance traveled will
     * depend on the initial velocity of the fling.
     *
     * @param startX    Starting point of the scroll (X)
     * @param startY    Starting point of the scroll (Y)
     * @param velocityX Initial velocity of the fling (X) measured in pixels per
     *                  second.
     * @param velocityY Initial velocity of the fling (Y) measured in pixels per
     *                  second
     * @param minX      Minimum X value. The scroller will not scroll past this point
     *                  unless overX > 0. If overfling is allowed, it will use minX as
     *                  a springback boundary.
     * @param maxX      Maximum X value. The scroller will not scroll past this point
     *                  unless overX > 0. If overfling is allowed, it will use maxX as
     *                  a springback boundary.
     * @param minY      Minimum Y value. The scroller will not scroll past this point
     *                  unless overY > 0. If overfling is allowed, it will use minY as
     *                  a springback boundary.
     * @param maxY      Maximum Y value. The scroller will not scroll past this point
     *                  unless overY > 0. If overfling is allowed, it will use maxY as
     *                  a springback boundary.
     * @param overX     Overfling range. If > 0, horizontal overfling in either
     *                  direction will be possible.
     * @param overY     Overfling range. If > 0, vertical overfling in either
     *                  direction will be possible.
     */
    public void fling(int startX, int startY, int velocityX, int velocityY,
                      int minX, int maxX, int minY, int maxY, int overX, int overY)
    {
        // Continue a scroll or fling in progress
        if (mFlywheel && !isFinished())
        {
            float oldVelocityX = mScrollerX.mCurrVelocity;
            float oldVelocityY = mScrollerY.mCurrVelocity;
            if (Math.signum(velocityX) == Math.signum(oldVelocityX) &&
                    Math.signum(velocityY) == Math.signum(oldVelocityY))
            {
                velocityX += oldVelocityX;
                velocityY += oldVelocityY;
            }
        }

        mMode = FLING_MODE;
        mScrollerX.fling(startX, velocityX, minX, maxX, overX);
        mScrollerY.fling(startY, velocityY, minY, maxY, overY);
    }

    /**
     * Notify the scroller that we've reached a horizontal boundary.
     * Normally the information to handle this will already be known
     * when the animation is started, such as in a call to one of the
     * fling functions. However there are cases where this cannot be known
     * in advance. This function will transition the current motion and
     * animate from startX to finalX as appropriate.
     *
     * @param startX Starting/current X position
     * @param finalX Desired final X position
     * @param overX  Magnitude of overscroll allowed. This should be the maximum
     *               desired distance from finalX. Absolute value - must be positive.
     */
    public void notifyHorizontalEdgeReached(int startX, int finalX, int overX)
    {
        mScrollerX.notifyEdgeReached(startX, finalX, overX);
    }

    /**
     * Notify the scroller that we've reached a vertical boundary.
     * Normally the information to handle this will already be known
     * when the animation is started, such as in a call to one of the
     * fling functions. However there are cases where this cannot be known
     * in advance. This function will animate a parabolic motion from
     * startY to finalY.
     *
     * @param startY Starting/current Y position
     * @param finalY Desired final Y position
     * @param overY  Magnitude of overscroll allowed. This should be the maximum
     *               desired distance from finalY. Absolute value - must be positive.
     */
    public void notifyVerticalEdgeReached(int startY, int finalY, int overY)
    {
        mScrollerY.notifyEdgeReached(startY, finalY, overY);
    }

    /**
     * Returns whether the current Scroller is currently returning to a valid position.
     * Valid bounds were provided by the
     * {@link #fling(int, int, int, int, int, int, int, int, int, int)} method.
     * <p/>
     * One should check this value before calling
     * {@link #startScroll(int, int, int, int)} as the interpolation currently in progress
     * to restore a valid position will then be stopped. The caller has to take into account
     * the fact that the started scroll will start from an overscrolled position.
     *
     * @return true when the current position is overscrolled and in the process of
     * interpolating back to a valid value.
     */
    public boolean isOverScrolled()
    {
        return ((!mScrollerX.mFinished &&
                mScrollerX.mState != SplineOverScroller.SPLINE) ||
                (!mScrollerY.mFinished &&
                        mScrollerY.mState != SplineOverScroller.SPLINE));
    }

    /**
     * Stops the animation. Contrary to {@link #forceFinished(boolean)},
     * aborting the animating causes the scroller to move to the final x and y
     * positions.
     *
     * @see #forceFinished(boolean)
     */
    public void abortAnimation()
    {
        mScrollerX.finish();
        mScrollerY.finish();
        if (mListener != null)
            mListener.onScrollStop();
    }

    /**
     * Returns the time elapsed since the beginning of the scrolling.
     *
     * @return The elapsed time in milliseconds.
     * @hide
     */
    public int timePassed()
    {
        final long time = AnimationUtils.currentAnimationTimeMillis();
        final long startTime = Math.min(mScrollerX.mStartTime, mScrollerY.mStartTime);
        return (int) (time - startTime);
    }

    /**
     * @hide
     */
    public boolean isScrollingInDirection(float xvel, float yvel)
    {
        final int dx = mScrollerX.mFinal - mScrollerX.mStart;
        final int dy = mScrollerY.mFinal - mScrollerY.mStart;
        return !isFinished() && Math.signum(xvel) == Math.signum(dx) &&
                Math.signum(yvel) == Math.signum(dy);
    }

    static class SplineOverScroller
    {
        // Initial position
        private int mStart;

        // Current position
        private int mCurrentPosition;

        // Final position
        private int mFinal;

        // Initial velocity
        private int mVelocity;

        // Current velocity
        private float mCurrVelocity;

        // Constant current deceleration
        private float mDeceleration;

        // Animation starting time, in system milliseconds
        private long mStartTime;

        // Animation duration, in milliseconds
        private int mDuration;

        // Duration to complete spline component of animation
        private int mSplineDuration;

        // Distance to travel along spline animation
        private int mSplineDistance;

        // Whether the animation is currently in progress
        private boolean mFinished;

        // The allowed overshot distance before boundary is reached.
        private int mOver;

        // Fling friction
        private float mFlingFriction = ViewConfiguration.getScrollFriction();

        // Current state of the animation.
        private int mState = SPLINE;

        // Constant gravity value, used in the deceleration phase.
        private static final float GRAVITY = 2000.0f;

        // A context-specific coefficient adjusted to physical values.
        private float mPhysicalCoeff;

        private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));
        private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)
        private static final float START_TENSION = 0.5f;
        private static final float END_TENSION = 1.0f;
        private static final float P1 = START_TENSION * INFLEXION;
        private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION);

        private static final int NB_SAMPLES = 100;
        private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1];
        private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1];

        private static final int SPLINE = 0;
        private static final int CUBIC = 1;
        private static final int BALLISTIC = 2;

        static
        {
            float x_min = 0.0f;
            float y_min = 0.0f;
            for (int i = 0; i < NB_SAMPLES; i++)
            {
                final float alpha = (float) i / NB_SAMPLES;

                float x_max = 1.0f;
                float x, tx, coef;
                while (true)
                {
                    x = x_min + (x_max - x_min) / 2.0f;
                    coef = 3.0f * x * (1.0f - x);
                    tx = coef * ((1.0f - x) * P1 + x * P2) + x * x * x;
                    if (Math.abs(tx - alpha) < 1E-5) break;
                    if (tx > alpha) x_max = x;
                    else x_min = x;
                }
                SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x;

                float y_max = 1.0f;
                float y, dy;
                while (true)
                {
                    y = y_min + (y_max - y_min) / 2.0f;
                    coef = 3.0f * y * (1.0f - y);
                    dy = coef * ((1.0f - y) * START_TENSION + y) + y * y * y;
                    if (Math.abs(dy - alpha) < 1E-5) break;
                    if (dy > alpha) y_max = y;
                    else y_min = y;
                }
                SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
            }
            SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
        }

        void setFriction(float friction)
        {
            mFlingFriction = friction;
        }

        SplineOverScroller(Context context)
        {
            mFinished = true;
            final float ppi = context.getResources().getDisplayMetrics().density * 160.0f;
            mPhysicalCoeff = SensorManager.GRAVITY_EARTH // g (m/s^2)
                    * 39.37f // inch/meter
                    * ppi
                    * 0.84f; // look and feel tuning
        }

        void updateScroll(float q)
        {
            mCurrentPosition = mStart + Math.round(q * (mFinal - mStart));
        }

        /*
         * Get a signed deceleration that will reduce the velocity.
         */
        static private float getDeceleration(int velocity)
        {
            return velocity > 0 ? -GRAVITY : GRAVITY;
        }

        /*
         * Modifies mDuration to the duration it takes to get from start to newFinal using the
         * spline interpolation. The previous duration was needed to get to oldFinal.
         */
        private void adjustDuration(int start, int oldFinal, int newFinal)
        {
            final int oldDistance = oldFinal - start;
            final int newDistance = newFinal - start;
            final float x = Math.abs((float) newDistance / oldDistance);
            final int index = (int) (NB_SAMPLES * x);
            if (index < NB_SAMPLES)
            {
                final float x_inf = (float) index / NB_SAMPLES;
                final float x_sup = (float) (index + 1) / NB_SAMPLES;
                final float t_inf = SPLINE_TIME[index];
                final float t_sup = SPLINE_TIME[index + 1];
                final float timeCoef = t_inf + (x - x_inf) / (x_sup - x_inf) * (t_sup - t_inf);
                mDuration *= timeCoef;
            }
        }

        void startScroll(int start, int distance, int duration)
        {
            mFinished = false;

            mCurrentPosition = mStart = start;
            mFinal = start + distance;

            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mDuration = duration;

            // Unused
            mDeceleration = 0.0f;
            mVelocity = 0;
        }

        void setScrollDuration(int duration)
        {
            mDuration = duration;
        }

        void finish()
        {
            mCurrentPosition = mFinal;
            // Not reset since WebView relies on this value for fast fling.
            // TODO: restore when WebView uses the fast fling implemented in this class.
            // mCurrVelocity = 0.0f;
            mFinished = true;
        }

        void setFinalPosition(int position)
        {
            mFinal = position;
            mFinished = false;
        }

        void extendDuration(int extend)
        {
            final long time = AnimationUtils.currentAnimationTimeMillis();
            final int elapsedTime = (int) (time - mStartTime);
            mDuration = elapsedTime + extend;
            mFinished = false;
        }

        boolean springback(int start, int min, int max)
        {
            mFinished = true;

            mCurrentPosition = mStart = mFinal = start;
            mVelocity = 0;

            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mDuration = 0;

            if (start < min)
            {
                startSpringback(start, min, 0);
            } else if (start > max)
            {
                startSpringback(start, max, 0);
            }

            return !mFinished;
        }

        private void startSpringback(int start, int end, int velocity)
        {
            // mStartTime has been set
            mFinished = false;
            mState = CUBIC;
            mCurrentPosition = mStart = start;
            mFinal = end;
            final int delta = start - end;
            mDeceleration = getDeceleration(delta);
            // TODO take velocity into account
            mVelocity = -delta; // only sign is used
            mOver = Math.abs(delta);
            mDuration = (int) (1000.0 * Math.sqrt(-2.0 * delta / mDeceleration));
        }

        void fling(int start, int velocity, int min, int max, int over)
        {
            mOver = over;
            mFinished = false;
            mCurrVelocity = mVelocity = velocity;
            mDuration = mSplineDuration = 0;
            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mCurrentPosition = mStart = start;

            if (start > max || start < min)
            {
                startAfterEdge(start, min, max, velocity);
                return;
            }

            mState = SPLINE;
            double totalDistance = 0.0;

            if (velocity != 0)
            {
                mDuration = mSplineDuration = getSplineFlingDuration(velocity);
                totalDistance = getSplineFlingDistance(velocity);
            }

            mSplineDistance = (int) (totalDistance * Math.signum(velocity));
            mFinal = start + mSplineDistance;

            // Clamp to a valid final position
            if (mFinal < min)
            {
                adjustDuration(mStart, mFinal, min);
                mFinal = min;
            }

            if (mFinal > max)
            {
                adjustDuration(mStart, mFinal, max);
                mFinal = max;
            }
        }

        private double getSplineDeceleration(int velocity)
        {
            return Math.log(INFLEXION * Math.abs(velocity) / (mFlingFriction * mPhysicalCoeff));
        }

        private double getSplineFlingDistance(int velocity)
        {
            final double l = getSplineDeceleration(velocity);
            final double decelMinusOne = DECELERATION_RATE - 1.0;
            return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);
        }

        /* Returns the duration, expressed in milliseconds */
        private int getSplineFlingDuration(int velocity)
        {
            final double l = getSplineDeceleration(velocity);
            final double decelMinusOne = DECELERATION_RATE - 1.0;
            return (int) (1000.0 * Math.exp(l / decelMinusOne));
        }

        private void fitOnBounceCurve(int start, int end, int velocity)
        {
            // Simulate a bounce that started from edge
            final float durationToApex = -velocity / mDeceleration;
            // The float cast below is necessary to avoid integer overflow.
            final float velocitySquared = (float) velocity * velocity;
            final float distanceToApex = velocitySquared / 2.0f / Math.abs(mDeceleration);
            final float distanceToEdge = Math.abs(end - start);
            final float totalDuration = (float) Math.sqrt(
                    2.0 * (distanceToApex + distanceToEdge) / Math.abs(mDeceleration));
            mStartTime -= (int) (1000.0f * (totalDuration - durationToApex));
            mCurrentPosition = mStart = end;
            mVelocity = (int) (-mDeceleration * totalDuration);
        }

        private void startBounceAfterEdge(int start, int end, int velocity)
        {
            mDeceleration = getDeceleration(velocity == 0 ? start - end : velocity);
            fitOnBounceCurve(start, end, velocity);
            onEdgeReached();
        }

        private void startAfterEdge(int start, int min, int max, int velocity)
        {
            if (start > min && start < max)
            {
                Log.e("OverScroller", "startAfterEdge called from a valid position");
                mFinished = true;
                return;
            }
            final boolean positive = start > max;
            final int edge = positive ? max : min;
            final int overDistance = start - edge;
            boolean keepIncreasing = overDistance * velocity >= 0;
            if (keepIncreasing)
            {
                // Will result in a bounce or a to_boundary depending on velocity.
                startBounceAfterEdge(start, edge, velocity);
            } else
            {
                final double totalDistance = getSplineFlingDistance(velocity);
                if (totalDistance > Math.abs(overDistance))
                {
                    fling(start, velocity, positive ? min : start, positive ? start : max, mOver);
                } else
                {
                    startSpringback(start, edge, velocity);
                }
            }
        }

        void notifyEdgeReached(int start, int end, int over)
        {
            // mState is used to detect successive notifications
            if (mState == SPLINE)
            {
                mOver = over;
                mStartTime = AnimationUtils.currentAnimationTimeMillis();
                // We were in fling/scroll mode before: current velocity is such that distance to
                // edge is increasing. This ensures that startAfterEdge will not start a new fling.
                startAfterEdge(start, end, end, (int) mCurrVelocity);
            }
        }

        private void onEdgeReached()
        {
            // mStart, mVelocity and mStartTime were adjusted to their values when edge was reached.
            // The float cast below is necessary to avoid integer overflow.
            final float velocitySquared = (float) mVelocity * mVelocity;
            float distance = velocitySquared / (2.0f * Math.abs(mDeceleration));
            final float sign = Math.signum(mVelocity);

            if (distance > mOver)
            {
                // Default deceleration is not sufficient to slow us down before boundary
                mDeceleration = -sign * velocitySquared / (2.0f * mOver);
                distance = mOver;
            }

            mOver = (int) distance;
            mState = BALLISTIC;
            mFinal = mStart + (int) (mVelocity > 0 ? distance : -distance);
            mDuration = -(int) (1000.0f * mVelocity / mDeceleration);
        }

        boolean continueWhenFinished()
        {
            switch (mState)
            {
                case SPLINE:
                    // Duration from start to null velocity
                    if (mDuration < mSplineDuration)
                    {
                        // If the animation was clamped, we reached the edge
                        mCurrentPosition = mStart = mFinal;
                        // TODO Better compute speed when edge was reached
                        mVelocity = (int) mCurrVelocity;
                        mDeceleration = getDeceleration(mVelocity);
                        mStartTime += mDuration;
                        onEdgeReached();
                    } else
                    {
                        // Normal stop, no need to continue
                        return false;
                    }
                    break;
                case BALLISTIC:
                    mStartTime += mDuration;
                    startSpringback(mFinal, mStart, 0);
                    break;
                case CUBIC:
                    return false;
            }

            update();
            return true;
        }

        /*
         * Update the current position and velocity for current time. Returns
         * true if update has been done and false if animation duration has been
         * reached.
         */
        boolean update()
        {
            final long time = AnimationUtils.currentAnimationTimeMillis();
            final long currentTime = time - mStartTime;

            if (currentTime == 0)
            {
                // Skip work but report that we're still going if we have a nonzero duration.
                return mDuration > 0;
            }
            if (currentTime > mDuration)
            {
                return false;
            }

            double distance = 0.0;
            switch (mState)
            {
                case SPLINE:
                {
                    final float t = (float) currentTime / mSplineDuration;
                    final int index = (int) (NB_SAMPLES * t);
                    float distanceCoef = 1.f;
                    float velocityCoef = 0.f;
                    if (index < NB_SAMPLES)
                    {
                        final float t_inf = (float) index / NB_SAMPLES;
                        final float t_sup = (float) (index + 1) / NB_SAMPLES;
                        final float d_inf = SPLINE_POSITION[index];
                        final float d_sup = SPLINE_POSITION[index + 1];
                        velocityCoef = (d_sup - d_inf) / (t_sup - t_inf);
                        distanceCoef = d_inf + (t - t_inf) * velocityCoef;
                    }

                    distance = distanceCoef * mSplineDistance;
                    mCurrVelocity = velocityCoef * mSplineDistance / mSplineDuration * 1000.0f;
                    break;
                }

                case BALLISTIC:
                {
                    final float t = currentTime / 1000.0f;
                    mCurrVelocity = mVelocity + mDeceleration * t;
                    distance = mVelocity * t + mDeceleration * t * t / 2.0f;
                    break;
                }

                case CUBIC:
                {
                    final float t = (float) (currentTime) / mDuration;
                    final float t2 = t * t;
                    final float sign = Math.signum(mVelocity);
                    distance = sign * mOver * (3.0f * t2 - 2.0f * t * t2);
                    mCurrVelocity = sign * mOver * 6.0f * (-t + t2);
                    break;
                }
            }

            mCurrentPosition = mStart + (int) Math.round(distance);

            return true;
        }
    }

    static class ViscousFluidInterpolator implements Interpolator
    {
        /**
         * Controls the viscous fluid effect (how much of it).
         */
        private static final float VISCOUS_FLUID_SCALE = 8.0f;

        private static final float VISCOUS_FLUID_NORMALIZE;
        private static final float VISCOUS_FLUID_OFFSET;

        static
        {

            // must be set to 1.0 (used in viscousFluid())
            VISCOUS_FLUID_NORMALIZE = 1.0f / viscousFluid(1.0f);
            // account for very small floating-point error
            VISCOUS_FLUID_OFFSET = 1.0f - VISCOUS_FLUID_NORMALIZE * viscousFluid(1.0f);
        }

        private static float viscousFluid(float x)
        {
            x *= VISCOUS_FLUID_SCALE;
            if (x < 1.0f)
            {
                x -= (1.0f - (float) Math.exp(-x));
            } else
            {
                float start = 0.36787944117f;   // 1/e == exp(-1)
                x = 1.0f - (float) Math.exp(1.0f - x);
                x = start + x * (1.0f - start);
            }
            return x;
        }

        @Override
        public float getInterpolation(float input)
        {
            final float interpolated = VISCOUS_FLUID_NORMALIZE * viscousFluid(input);
            if (interpolated > 0)
            {
                return interpolated + VISCOUS_FLUID_OFFSET;
            }
            return interpolated;
        }
    }
}
